The importance of the vitamin D in the biological systems of higher animals has been recognized since its discovery by Mellanby in 1920 (Mellanby, E. (1921) Spec. Rep. Ser. Med Res. Council (GB) SRS 61:4). It was in the interval of 1920-1930 that vitamin D officially became classified as a xe2x80x9cvitaminxe2x80x9d that was essential for the normal development of the skeleton and maintenance of calcium and phosphorous homeostasis.
Studies involving the metabolism of vitamin D3 (cholecalciferol) were initiated with the discovery and chemical characterization of the plasma metabolite, 25-hydroxyvitamin D3 [25(OH)D3] (Blunt, J. W. et al. (1968) Biochemistry 6:3317-3322) and the hormonally active form, 1xcex1,25(OH)2D3 (Myrtle, J. F. et al. (1970) J. Biol. Chem. 245:1190-1196; Norman, A. W. et al. (1971) Science 173:51-54; Lawson, D. E. M. et al (1971) Nature 230:228-230; Holick, M. F. (1971) Proc. Natl. Acad. Sci. USA 68:803-804). The formulation of the concept of a vitamin D endocrine system was dependent both upon appreciation of the key role of the kidney in producing 1xcex1, 25(OH)2D3 in a carefully regulated fashion (Fraser, D. R. and Kodicek, E (1970) Nature 288:764-766; Wong, R. G. et al. (1972) J. Clin. Invest. 51:1287-1291), and the discovery of a nuclear receptor for 1xcex1,25(OH)2D3 (VD3R) in the intestine (Haussler, M. R. et al. (1969) Exp. Cell Res. 58:234-242; Tsai, H. C. and Norman, A. W. (1972) J. Biol. Chem. 248:5967-5975). The operation of the vitamin D endocrine system depends on the following: first, on the presence of cytochrome P450 enzymes in the liver (Bergman, T. and Postlind, H. (1991) Biochem. J. 276:427-432; Ohyama, Y and Okuda, K. (1991) J. Biol. Chem. 266:8690-8695) and kidney (Henry, H. L. and Norman, A. W. (1974) J. Biol. Chem. 249:7529-7535; Gray, R. W. and Ghazarian, J. G. (1989) Biochem. J. 259:561-568), and in a variety of other tissues to effect the conversion of vitamin D3 into biologically active metabolites such as 1xcex1,25(OH)2D3 and 24R,25(OH)2D3; second, on the existence of the plasma vitamin D binding protein (DBP) to effect the selective transport and delivery of these hydrophobic molecules to the various tissue components of the vitamin D endocrine system (Van Baelen, H. et al. (1988) Ann NY Acad. Sci. 538:60-68; Cooke, N. E. and Haddad, J. G. (1989) Endocr. Rev. 10:294-307; Bikle, D. D. et al. (1986) J. Clin. Endocrinol. Metab. 63:954-959); and third, upon the existence of stereoselective receptors in a wide variety of target tissues that interact with the agonist 1xcex1,25(OH)2D3 to generate the requisite specific biological responses for this secosteroid hormone (Pike, J. W. (1991) Annu. Rev. Nutr. 11:189-216). To date, there is evidence that nuclear receptors for 1xcex1,25(OH)2D3 (VD3R) exist in more than 30 tissues and cancer cell lines (Reichel, H. and Norman, A. W. (1989) Annu. Rev. Med. 40:71-78).
Vitamin D3 and its hormonally active forms are well-known regulators of calcium and phosphorous homeostasis. These compounds are known to stimulate, at least one of, intestinal absorption of calcium and phosphate, mobilization of bone mineral, and retention of calcium in the kidneys. Furthermore, the discovery of the presence of specific vitamin D receptors in more than 30 tissues has led to the identification of vitamin D3 as a pluripotent regulator outside its classical role in calcium/bone homeostasis. A paracrine role for 1xcex1,25(OH)2D3 has been suggested by the combined presence of enzymes capable of oxidizing vitamin D3 into its active forms, e.g., 25-OHD-1xcex1-hydroxylase, and specific receptors in several tissues such as bone, keratinocytes, placenta, and immune cells. Moreover, vitamin D3 hormone and active metabolites have been found to be capable of regulating cell proliferation and differentiation of both normal and malignant cells (Reichel, H. et al. (1989) Ann. Rev. Med. 40: 71-78).
Given the pluripotent activities of vitamin D3 and its metabolites, much attention has focused on the development of synthetic analogs of these compounds. However, clinical applications of vitamin D3 and its structural analogs have been limited by the undesired side effects elicited by these compounds after administration to a subject, such as the deregulation of calcium and phosphorous homeostasis in vivo that results in hypercalcemia.
The present invention is based, at least in part, on the discovery of vitamin D3 compounds having a cyclic ether side chain, referred to hereinafter as xe2x80x9ccyclic ether vitamin D3 compoundsxe2x80x9d, and which are represented by the formula I. This invention also describes 3-epi forms of 1xcex1-hydroxy-vitamin D3 compounds, which are represented by the formula II. The cyclic ether and 1xcex1-hydroxy-vitamin D3 compounds of formulas I and II, respectively, referred to hereinafter as xe2x80x9cvitamin D3 compounds of formulas I and IIxe2x80x9d can be produced in vivo via a pathway which catalyzes the epimerization 3-xcex2-hydroxy-vitamin D3 in certain tissues, e.g., keratinocytes, bone cells. The vitamin D3 compounds of the present invention can be used as substitutes for natural and synthetic forms of vitamin D3.
Accordingly, the present invention pertains to cyclic ether vitamin D3 compounds having the formula (I) as follows: 
wherein A1, A2 and A3 represent a single or a double bond; X, R1, R2, R3, R4 and R5 can, e.g., be chosen individually from the group of: a hydrogen, a halogen, a haloalkyl, a hydroxy, a hydroxy-protecting group, an alkyl, e.g., a lower alky, an alkenyl, an alkynyl, an alkoxy, an aryl group and a heterocyclic group. The orientation of the X group can be in either an xcex1- or a xcex2-configuration.
In a preferred embodiment, the cyclic ether vitamin D3 compound is in its 3-epi configuration, wherein the orientation of the X group on the A-ring is in an xcex1-configuration.
The present invention also pertains to 3-epi forms of 1xcex1-hydroxy-vitamin D3 compounds having the formula II as follows: 
wherein A1 represents a single, a double, e.g., a trans-double, a cis-double, or a triple bond; A2, A3 and A4 represent a single or a double bond; R2, R3, R4, R7, R8 and R9 can, e.g., be chosen individually from the group of: a hydrogen, a deuterium, a deuteroalkyl, a hydroxy, an alkyl, e.g., a lower alkyl, e.g., a C1-C4 alkyl, an alkoxide, an O-acyl, a halogen, e.g., a fluoride, a haloalkyl (e.g., a fluoroalkyl, xe2x80x94CF3), a hydroxyalkyl, e.g., a hydroxyalkyl wherein the alkyl group is a C4-C10 alkyl, an amine or a thiol group, and wherein the pairs of R2 and R3, or R4 and R7 taken together can be an oxygen atom, e.g., as in a carbonyl moiety 
and R5 and R6 can, e.g., each be chosen individually from the group of: a hydrogen, a deuterium, a halogen, e.g., a fluoride, an alkyl, e.g., a lower alkyl, e.g., a C1-C4 alkyl, a hydroxyalkyl, a haloalkyl, e.g., a fluoroalkyl, and a deuteroalkyl. The amine or thiol group of R2, R3, R4, R7, R8 and R9 can be substituted to form, e.g., a primary or a secondary amine, or a primary or secondary thiol, wherein the substituents can be an alkyl or an aryl group, e.g., a substituent having 2- to 10-carbon atoms.
In another aspect, the present invention further pertains to a pharmaceutical composition comprising, a therapeutically effective amount of a vitamin D3 compound having the formulas I or II, and a pharmaceutically acceptable carrier.
In yet another aspect, this invention provides a method of modulating a biological activity of a vitamin D3-responsive cell. This method comprising contacting the cell with an effective amount of an isolated vitamin D3 compound of formulas I and II such that modulation of the activity of the cell occurs.
Another aspect of the invention provides a method of treating in a subject, a disorder characterized by aberrant growth or activity of a cell, comprising administering to the subject an effective amount of a pharmaceutical composition of a vitamin D3 compound of formulas I and II such that the growth or activity of the cell is reduced.
In a preferred embodiment, the vitamin D3 compound of formulas I and II used in the treatment has improved biological properties compared to vitamin D3, such as enhanced stability and/or reduced toxicity.
In one aspect, a method for inhibiting the proliferation and/or an inducing the differentiation of a hyperproliferative skin cell is provided, wherein the hyperproliferative skin cell can be an epidermal cell or an epithelial cell. Accordingly, therapeutic methods for treating hyperproliferative skin disorders, e.g., psoriasis, are provided.
In certain embodiments, the instant method can be used for the treatment of, or prophylactic prevention of a disorder characterized by aberrant cell growth of vitamin D3-responsive neoplastic cell, e.g., by administering a pharmaceutical preparation of a vitamin D3 compound having the formula as shown in I or II in an amount effective to inhibit growth of the neoplastic cells.
In another aspect, the subject method can be used to modulate an immune response, comprising administering to a subject a pharmaceutical preparation of a vitamin D compound so as to alter immune function in the subject. In one embodiment, the method can be used in the treatment of lymphoid cells, e.g., T cells, natural killer cells, so as to suppress immune reactions, e.g., to decrease T cell activity, e.g., to decrease production of lymphokines such as IL-2 and IFN-xcex3, to decrease T cell proliferation. In preferred embodients, the method can be used in treating graft rejection, autoimmunity and inflammation.
In yet another aspect, the vitamin D3 compound of the present invention are useful in the treatment of disorder characterized by a deregulation of calcium and phosphate metabolism, comprising administering to a subject a pharmaceutical preparation of a vitamin D3 compounds of formulas I and II so as to ameliorate the deregulation in calcium and phosphate metabolism.
In a preferred embodiment, the disorder is osteoporosis. In other embodiments, the vitamin D3 compounds of formulas I and II can be used to treat diseases characterized by other deregulations in the metabolism of calcium and phosphate.
In another aspect, a method for inhibiting PTH secretion in parathyroid cell using the vitamin D3 compound of formulas I and II is provided. Furthermore, therapeutic methods for treating secondary hyperparathyroidism are also provided.
In yet another aspect, the present invention provides a method of preventing or protecting against neuronal loss by contacting a vitamin D3-responsive cell, e.g., a neuronal cell, with a vitamin D3 compound of formulas I and II to prevent or retard neuron loss.
In yet another aspect, the present invention provides a method of modulating the activity of a vascular smooth muscle cell by contacting a vitamin D3-responsive smooth muscle cell with a vitamin D3 compound of formulas I and II to activate or, preferably, inhibit the activity of the cell.